Technologies for uniformly irradiating a predetermined plane with laser light emitted from a light source such as a semiconductor laser have conventionally been proposed. For example, in a light irradiation apparatus in which a plurality of cylindrical lenses in a cylindrical lens array divide laser light incident from a light source part into a plurality of light fluxes and another lens superimposes irradiation regions of the light fluxes on one another on an irradiation plane, an optical path length difference generation part is provided between the light source part and the cylindrical lens array. The optical path length difference generation part includes a plurality of transparent parts that produce differences in optical path length among them that are longer than the coherence length (coherence distance) of the laser light, and light that has passed through the plurality of transparent parts respectively enters the plurality of cylindrical lenses. This prevents interference fringes from appearing and achieves uniformity of the intensity distribution of illumination light that is emitted onto the irradiation plane (see, for example, Japanese Patent Application Laid-Open No. 2004-12757 as one example of such an apparatus).
The above-described light irradiation apparatus is provided with a light condensing part that, in the case of making a linear cross section of light on the irradiation plane, causes the plurality of light fluxes to converge on the same position of the irradiation plane when viewed in the direction of arrangement of the cylindrical lenses. However, in the case where parallelism of the entrance and exit surfaces of the transparent part varies among the transparent parts or parallelism of the entrance and exit surfaces of the cylindrical lens varies among the cylindrical lenses when viewed in the above direction of arrangement, the light condensing positions of the plurality of light fluxes on the irradiation plane will be shifted from one another in a direction perpendicular to the arrangement direction. Such shifts in the light condensing positions of the light fluxes reduce the quality of illumination light and, for example, with a drawing apparatus that uses the light irradiation apparatus, reduce the accuracy of pattern drawing.